Confluences

The previous post was mostly devoted to the Fluvial Network calculation and rivers rendering was not covered enough. I stayed on the straightforward and even unexpected solution: draw rivers based on their length only. It’s rather elegant, but tributaries don’t increase the main stem volume and this may be a problem. In real world tributaries usually don’t do it too, at least not in a direct way. But from a world-building perspective my implementation looks a bit boring. I want rivers to be not so predictable.

The problem is that we had amended rivers with bends and rivers’ control points don’t coincide with map polygons anymore. Usually we have 3 river elements for a polygon, so we need to interpolate the related polygon’s flux to have different width for each element.

Another solution is to combine flux and length approaches. On a regular stream width should get constantly increasing based on length, but on confluence river width should be completely recalculated based on the polygon’s flux value.

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River systems

Now it’s a good time to draw some rivers. As we already have a heightmap we do not need to fabricate rivers out of nothing and will calculate river systems based on precipitation drainage.

The first step is to build a precipitation model. Frankly speaking, we can omit this step and consider that each cell has the same precipitation. It will be enough to create plausible rivers, but having a precipitation model is useful not only for rivers calculation, but also for biomes and erosion modeling.

The most interesting precipitation model I know is the Wind model presented by Scott Turner. Here he shows how it can be easily used for biomes definition and here disclose a few info regarding rivers. Despite this model is cool, it’s a bit over-complicated for a landscapes created via blobs approach and requires more detailed map.

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